Electronic display technology for displaying graphical images and/or text has evolved dramatically to meet the pervasive user demand for more realistic and interactive displays. A wide range of display technologies with differing capabilities are now available including: cathode ray tube (CRT); bistable display; electronic paper; nixie tube displays; vector display; flat panel display; vacuum fluorescent display (VF); light-emitting diode (LED) displays; ELD; plasma display panels (PDP); liquid crystal display (LCD) such as HPA display and thin-film transistor displays (TFT); organic light-emitting diode displays (OLED); surface-conduction electron-emitter display (SED) (experimental); laser TV (forthcoming); carbon nanotubes (experimental); and nanocrystal displays (experimental) which use quantum dots to make vibrant, flexible screens.
Further adaptations have been made to achieve enhanced visual effects using this technology, e.g. Stereoscopic and Multi-Layer Displays (MLD). Stereoscopic and auto stereoscopic displays provide the appearance of a 3D image by providing slightly different visual images to the left and right eyes of the viewer to utilize the binocular capabilities of the human visual system.
MLD systems use multiple layered screens aligned parallel with each other in a stacked arrangement with a physical separation between each screen. Each screen is capable of displaying images. Thus, multiple images separated by a physical separation or “depth” can be displayed on one display. PCT Publication No. WO 99/42889 discloses such an MLD in which depth is created by displaying images on the background screen furthest from the viewer which will appear at some depth behind images displayed on the screen(s) closer to the user. The benefits of MLDs, in particular those utilizing the technology described in the PCT Publication Nos. WO 99/42889 and WO 99/44095 are gaining increasingly widespread recognition and acceptance due to their enhanced capabilities compared to conventional single focal plane displays (SLD).
The benefits of MLDs are especially germane to displays using liquid crystal displays (LCD), though MLDs can also be formed using other display technologies, e.g. an LCD front screen may be layered in front of an OLED rear screen.
There are two main types of Liquid Crystal Displays used in computer monitors, passive matrix and active matrix. Passive-matrix Liquid Crystal Displays use a simple grid to supply the charge to a particular pixel on the display. Creating the grid starts with two glass layers called substrates. One substrate is given columns and the other is given rows made from a transparent conductive material. This is usually indium tin oxide. The rows or columns are connected to integrated circuits that control when a charge is sent down a particular column or row. The liquid crystal material is sandwiched between the two glass substrates, and a polarizing film is added to the outer side of each substrate.
A pixel is defined as the smallest resolvable area of an image, either on a screen or stored in memory. Each pixel in a monochrome image has its own brightness, from 0 for black to the maximum value (e.g. 255 for an eight-bit pixel) for white. In a color image, each pixel has its own brightness and color, usually represented as a triple of red, green and blue intensities. To turn on a pixel, the integrated circuit sends a charge down the correct column of one substrate and a ground activated on the correct row of the other. The row and column intersect at the designated pixel and that delivers the voltage to untwist the liquid crystals at that pixel.
The passive matrix system has significant drawbacks, notably slow response time and imprecise voltage control. Response time refers to the Liquid Crystal Displays ability to refresh the image displayed. Imprecise voltage control hinders the passive matrix's ability to influence only one pixel at a time. When voltage is applied to untwist one pixel, the pixels around it also partially untwist, which makes images appear fuzzy and lacking in contrast. Active-matrix Liquid Crystal Displays depend on thin film transistors (TFT). Thin film transistors are tiny switching transistors and capacitors. They are arranged in a matrix on a glass substrate.
To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle. And if the amount of voltage supplied to the crystal is carefully controlled, it can be made to untwist only enough to allow some light through. By doing this in very exact, very small increments, Liquid Crystal Displays can create a grey scale.
Most displays today offer 256 levels of brightness per pixel. A Liquid Crystal Display that can show colors must have three sub-pixels with red, green and blue color filters to create each color pixel. Through the careful control and variation of the voltage applied, the intensity of each sub-pixel can range over 256 shades. Combining the sub-pixel produces a possible palette of 16.8 million colors (256 shades of red×256 shades of green×256 shades of blue). Liquid Crystal Displays employ several variations of liquid crystal technology, including super twisted nematics, dual scan twisted nematics, ferroelectric liquid crystal and surface stabilized ferroelectric liquid crystal. They can be lit using ambient light in which case they are termed as reflective, backlit and termed transmissive, or a combination of backlit and reflective and called transflective.
There are also emissive technologies such as Organic Light Emitting Diodes, and technologies which project an image directly onto the back of the retina which are addressed in the same manner as Liquid Crystal Displays. These devices are described hereafter as LCD panels.
However, the adoption of many display content types, including display content for stereoscopic and MLD displays has been hampered by the need to custom-build computer software applications and display controllers to suit the particular display-type. For example, a user that has an MLD may be limited to using custom designed software and hardware controllers as the MLD software and controllers may not be able to display other types of display content correctly. Conversely, the MLD software and controllers are purpose-built for the MLD and thus images designed for an MLD generally cannot be displayed correctly on SLDs or stereoscopic displays.